As a typical example of a photopolymerization initiator used in a photoresist composition, there have been know various types such as acetophenone derivatives, benzophenone derivatives, triazine derivatives, biimidazole derivatives, acylphosphine oxide derivatives and oxime ester derivatives, and among them, oxime ester derivatives have advantages; they absorb ultraviolet light almost without color and have high radical generation efficiency and good compatibility with photoresist composition materials and outstanding stability. However, oxime derivative compounds developed at an early stage have low photoinitiation efficiency, and especially, need to increase an exposure dose due to low sensitivity in a pattern exposure process, causing production amount reductions.
Thus, development of a photopolymerization initiator with high photosensitivity leads to achievement of sufficient sensitivity in small amounts, producing a cost saving effect, and exposure dose reductions due to high sensitivity, increasing a production amount.
A variety of oxime ester compound derivatives of formula 2 that can be used as a photopolymerization initiator in a photoresist composition are already known.

In the case of a photopolymerization initiator having an oxime ester group, it is easy to synthesize a variety of photopolymerization initiators capable of adjusting their absorption area by introducing appropriate substituents at R, R′ and R″ of a compound.
The oxime ester compound can polymerize and cure a polymerizable compound having an unsaturated bond when the photoresist composition is irradiated with light at 365-435 nm, and is being used for a black matrix, a color filter, a column spacer, an organic insulator film, and a photoresist composition for overcoating.
Accordingly, there has been a continuous demand for a novel photoinitiator that is suitable for a variety of uses because it satisfies the industrial requirements such as high sensitivity to a light source of long wavelengths of 365-435 nm and good photopolymerization reactivity, easy to manufacture, high thermal stability and storage stability, making it easy to handle, and a satisfactory solubility in a solvent (propylene glycol monomethyl ether acetate (PGMEA).
Recently, intensive research is being done on a photoresist composition used in a thin film display such as a liquid crystal display and an organic light emitting diode (OLED), to be more specific, a photoresist composition containing a high sensitivity photopolymerization initiator capable of forming a pattern for an organic insulator film of a liquid crystal display such as a thin film transistor liquid crystal display (TFT-LCD), a column spacer, an UV overcoat, R.G.B. color resist and a black matrix during development using an alkali developer solution.
Generally, a resist composition used to form a pattern preferably includes a photoresist composition containing a binder resin, a multifunctional monomer having an ethylenically unsaturated bond, and a photopolymerization initiator.
However, when forming a pattern using a conventional photopolymerization initiator, it needs to increase an amount of the photopolymerization initiator or an exposure dose due to low sensitivity in an exposure process for pattern formation, and its resulting disadvantage is that a mask is contaminated during the exposure process and by-products generated after decomposition of the photopolymerization initiator during crosslinking at high temperature reduce yields, and there is a production amount reduction problem due to the exposure process time increasing with the increasing exposure dose, and therefore, efforts are being made to solve the problems.